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For the former ethnological term Hamites see Hamitic. Hamitic is an obsolete ethno-linguistic classification of some Ethnic groups within the Afro-Asiatic (previously termed "Hamito-Semitic" language family
Hamites
Fossil range: Early - Late Cretaceous
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ammonitida
Suborder: Ancyloceratina
Family: Hamitidae
Genus: Hamites
Subgenera

Eohamites
Hamitella
Helicohamites
Lytohamites
Planohamites
Psilohamites
Sziveshamites

Hamites ("Hook-stone") is a genus of heteromorph ammonite that evolved late in the Aptian stage of the Early Cretaceous and lasted into the Cenomanian stage of the Late Cretaceous. The Early Cretaceous ( timestratigraphic name or the Lower Cretaceous ( logstratigraphic name is the earlier of the two major divisions of the Cretaceous Late Cretaceous (100mya - 65mya refers to the second half of the Cretaceous Period, named after the famous white Chalk cliffs of southern England The Cretaceous (kriːˈteɪʃəs, usually abbreviated 'K' for its German translation "Kreide" is a geologic period and system, reaching from the end of Molluscs are animals belonging to the phylum Mollusca. There are around 250000 extant Species within the phylum with an estimated 70000 The cephalopods ( Greek plural (kephalópoda "head-feet" are the Mollusc class Cephalopoda characterized by Ammonites are an extinct group of marine animals of the subclass Ammonoidea in the class Cephalopoda phylum Ammonites are an extinct group of marine animals of the subclass Ammonoidea in the class Cephalopoda phylum The Ancyloceratina were a diverse suborder of Ammonite most closely related to the ammonites of order Lytoceratina. In Biology, a subgenus is a Taxonomic rank directly below Genus. A genus (plural genera from Γένος Latin genus "descent family type gender" is a low-level Taxonomic Ammonites are an extinct group of marine animals of the subclass Ammonoidea in the class Cephalopoda phylum Aptian stage is a Faunal stage of the Early Cretaceous epoch in the Geologic timescale, that extends from 125 The Early Cretaceous ( timestratigraphic name or the Lower Cretaceous ( logstratigraphic name is the earlier of the two major divisions of the Cretaceous |-|The Cenomanian age (also known as Woodbinian by the [[ICS]] is the first or earliest or oldest Geochronological "geologic age" Late Cretaceous (100mya - 65mya refers to the second half of the Cretaceous Period, named after the famous white Chalk cliffs of southern England The genus is almost certainly paraphyletic but remains in wide use as a "catch all" for heteromorph ammonites of the superfamily Turrilitaceae that do not neatly fit into the more derived groupings. In Phylogenetics, a group of organisms is said to be paraphyletic if the group contains its most recent common ancestor but does not contain all The Ancyloceratina were a diverse suborder of Ammonite most closely related to the ammonites of order Lytoceratina. Superfamily Turrilitaceae ("Tower Stones" was a superfamily of heteromorph Ammonites of the suborder Ancyloceratina that lived during the Cretaceous In Phylogenetics, a trait is derived if it is present in an organism but was absent in the last common ancestor of the group being considered In an attempt to identify clades within the genus, it has been divided up into a series of new genera or subgenera by different palaeontologists, including Eohamites, Hamitella, Helicohamites, Lytohamites, Planohamites, Psilohamites, and Sziveshamites. A clade is a taxonomic group comprising a single Common ancestor and all the descendants of that ancestor Palaeontology redirects here For the Scientific journal, see Palaeontology (journal. [1] [2]

The type species is Hamites attenuatus from the early Albian, named by James Sowerby in his Mineral Conchology of Great Britain of 1814, although the genus itself was created by James Parkinson in his 1811 book Organic Remains of the Former World. James Sowerby ( March 21, 1757 - October 25, 1822) was an English naturalist and illustrator James Parkinson may also refer to James Parkinson (1730-1813, the museum proprietor and land agent This James Parkinson is best known as the first scientific description of a disease he called the Shaking Palsy, now referred to as Parkinson's disease in his honour. Parkinson's disease (also known as Parkinson disease or PD) is a degenerative disorder of the Central nervous system that often impairs the sufferer's [3]

Contents

Morphology and ecology

Hamites species are characterised by a shell that began with an open, sometimes helical, regular spiral that either opened into a single large hook [6], or else formed three parallel shafts that gave the mature shell the approximate appearance of a paper clip [7]. A paper clip (or sometimes paperclip) is a device which holds several sheets of Paper together by means of Pressure: it leaves the paper intact and No Hamites had spines or other such ornamentation on the shell, but several species appear to have developed apertural modifications when mature; that is, once the ammonite had grown to its final size, the aperture became constricted and was bounded by one or two thickened ribs, known as collars. These have been observed on other ammonites as well, and are assumed to be signs of sexual dimorphism. Sexual dimorphism is the systematic difference in form between individuals of different Sex in the same Species. [4] [5].

The open shell of these ammonites would have made them poor swimmers because of drag, but beyond that fact, very little is certain about their mode of life. In Fluid dynamics, drag (sometimes called fluid resistance) is the force that resists the movement of a Solid object through a Fluid (a It is widely assumed that they were planktonic, perhaps catching small prey in the manner of jellyfish, but repaired shell damage apparently caused by crabs may indicate that they spent at least some time close to the sea floor. Plankton consist of any drifting Organisms ( Animals Plants Archaea, or Bacteria) that inhabit the Pelagic zone of Jellyfish are free-swimming members of the phylum Cnidaria. They have several different basic morphologies that represent several different cnidarian classes including the [6] [7]

Phylogeny

The genus Hamites is of particular interest to palaeontologists because the species included in the genus span a wide range of morphologies including ones apparently similar to several more derived groups of heteromorph ammonites. In Phylogenetics, a trait is derived if it is present in an organism but was absent in the last common ancestor of the group being considered The genus rapidly diversified during the Albian into a number of morphologically distinct lineages that seem to have given rise to at least three other families of heteromorphs, the Baculitidae, Turrilitidae, and Scaphitidae. An evolutionary radiation is an increase in taxonomic diversity or morphological disparity due to adaptive change or the opening of ecospace Albian ( French Albion, from Alba = Aube in France) is a stage of the Cretaceous period. Baculites ("walking stick rock" is a Genus of extinct marine animals in the Phylum Mollusca and Class Scaphites ( Greek skafh, "a boat or anything dug or scooped out" is a Genus of extinct Cephalopod belonging to the [8] [9] The lineage that gave rise to the helical Turrilitidae, for example, had a shell that initially grew as a helix before straightening out; the Turrilitidae thus appear to have been derived from neotenic Hamites that retained the helically-coiled juvenile morphology of Hamites into adulthood. Neoteny (niːˈɒtɨniː also called juvenilization, is the retention by adults in a species of traits previously seen only in juveniles ( pedomorphosis/paedomorphosis [10]

References

  1. ^ Szives O. & Monks N. 2002. Heteromorphs of the Tata Limestone Formation (Aptian - Lower Albian), Hungary. Palaeontology, 44, 1137-1149 [1]
  2. ^ Monks N. 2002. Cladistic analysis of a problematic ammonite group: the Hamitidae (Cretaceous, Albian - Turonian) and proposals for new cladistic terms. Palaeontology, 44, 687-707 [2]
  3. ^ Parkinson J (2002). "An essay on the shaking palsy. 1817." (Reproduced\). J Neuropsychiatry Clin Neurosci 14 (2): 223-36; discussion 222. PMID 11983801.  
  4. ^ Monks N. 1999. Cladistic analysis of Albian heteromorph ammonites. Palaeontology, 42, 907-925 [3]
  5. ^ Monks N. 2002. Cladistic analysis of a problematic ammonite group: the Hamitidae (Cretaceous, Albian - Turonian) and proposals for new cladistic terms. Palaeontology, 44, 687-707 [4]
  6. ^ Trueman A. 1941. The ammonite body-chamber, with special reference to the buoyancy and mode of life of the living animal. Quarterly Journal of the Geological Society of London, 384, 339-383
  7. ^ Monks N. 2000. Mid Cretaceous heteromorph ammonite shell damage. Journal of Molluscan Studies, 66, 283-285
  8. ^ Monks N. 1999. Cladistic analysis of Albian heteromorph ammonites. Palaeontology, 42, 907-925 [5]
  9. ^ Monks N. 2000. Phylogeny of the Scaphitidae. Journal of Molluscan Studies, 66, 205-216
  10. ^ Monks N. 2001. The functional morphology of Hamites and Stomohamites and the origins of the Turrilitidae. Bollettino Malacologico, 36, 195-200

See also

External links

Baculites ("walking stick rock" is a Genus of extinct marine animals in the Phylum Mollusca and Class Scaphites ( Greek skafh, "a boat or anything dug or scooped out" is a Genus of extinct Cephalopod belonging to the
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